Usually in a vehicle occupant restraint device of this type, a gas bag is to be inflated as rapidly as possible with gas that is produced by a gas generator. However, in certain cases, it is desirable not to inflate the gas bag with the entire available gas volume or, more generally, to discharge gas, discharge openings, whose release makes it possible to limit the pressure in the gas bag, being provided in the gas bag module for this purpose.
In the literature, numerous solutions are described that have the goal, in the event of an accident, of regulating the interior pressure and thus the restraining effect of the gas bag as a function of the load condition, possible control parameters being the mass of the person being protected or the travel velocity, to name but a few. Among the solutions are apparatuses having rotating or sliding valves, which regulate the gas flow. Another approach, disclosed in DE 198 10 537 A1, lies in limiting the gas flow from the gas generator into the gas bag as a function of the load condition, in that a valve is activated by an adjusting means during driving, before an accident takes place.
Another solution provides for limiting the achievable interior pressure by creating a (further) discharge opening in the gas bag, in addition to any already present, and to close it off using a diaphragm. The diaphragm will then burst in response to a specific pressure, and gas can be discharged from the gas bag (for example, DE 296 17 586).
One disadvantage in the valve solutions that are known from the prior art lies in the fact that they generally can only be realized at significant manufacturing expense. If the goal is to regulate the flow of gases from the gas bag, there is also the problem of the very short response times that are required by the regulator, because the entire process during which the gas bag inflates and the occupant plunges into it and is thrown back takes less than 150 ms. On the other hand, if the attempt is made to control or to regulate the quantity of gas that flows into the gas bag by limiting the gas flow by a valve, then the inflation time is also increased, so that the person being protected may be provided with the full restraining effect only at a later point in time. Solutions that operate on the basis of a bursting diaphragm do not have the problem of response times, but they also do not represent regulating functions in the true sense of the word because they only react to a threshold value, i.e., when a specific interior pressure is reached.
In contrast, the present invention provides a system that, on the one hand, reacts with extremely short response times to the interior pressure within the gas bag, which increases during the inflation process, and that, on the other hand, makes it possible to set the maximum permissible interior pressure in stepwise fashion as a function of the existing load condition.